NCP1595, NCP1595A, NCP1595C

http://onsemi.com

10

PROTECTIONS

Undervoltage Lockout (UVLO)

The under voltage lockout feature prevents the controller

from switching when the input voltage is too low to power

the internal power supplies and reference. Hysteresis must

be incorporated in the UVLO comparator to prevent IxR

drops in the wiring or PCB traces from causing ON/OFF

cycling of the controller during heavy loading at power up

or power down.

Overcurrent Protection (OCP)

NCP1595/A/C detects high side switch current and then

compares to a voltage level representing the overcurrent

threshold limit. If the current through the high side FET

exceeds the overcurrent threshold limit for seven

consecutive switching cycles, overcurrent protection is

triggered.

Once the overcurrent protection occurs, hiccup mode

engages. First, hiccup mode, turns off both FETs and

discharges the internal compensation network at the output

of the OTA. Next, the IC waits typically 2 ms and then resets

the overcurrent counter. After this reset, the circuit attempts

another normal soft−start. During soft−start, the overcurrent

protection threshold is increased to prevent false

overcurrent detection while charging the output capacitors.

Hiccup mode reduces input supply current and power

dissipation during a short circuit. It also allows for much

improved system up−time, allowing auto−restart upon

removal of a temporary short−circuit.

Power Save Mode

If the load current decreases, the converter can skip

switching and operate with reduced frequency. This

minimizes the quiescent current and maintains high

efficiency. NCP1595C disables this feature.

Pre−Bias Startup

In some applications the controller will be required to start

switching when it’s output capacitors are charged anywhere

from slightly above 0 V to just below the regulation voltage.

This situation occurs for a number of reasons: the

converter’s output capacitors may have residual charge on

them or the converter’s output may be held up by a low

current standby power supply. NCP1595/A/C supports

pre−bias start up by holding switching off until the soft−start

ramp reaches the FB Pin voltage.

Thermal Shutdown

The NCP1595/A/C protects itself from over heating with

an internal thermal monitoring circuit. If the junction

temperature exceeds the thermal shutdown threshold both

the upper and lower MOSFETs will be shut OFF.